Hydrocarbon isomerization catalyst

ABSTRACT

ISOMERIZABLE HYDROCARBONS ARE ISOMERIZED USING A CATALYTIC COMPOSITE COMPRISING A COMBINATION FO A PLATINUM GROUP COMPONENT AND A TIN COMPONENT WITH A POROUS CARRIER MATERIAL. A CATALYTIC COMPOSITE COMPRISING A PLATINUM GROUP METALLIC COMPONENT, A TIN COMPONENT AND A FRIEDEL-CRAFTS METAL HALIDE COMPONENT COMBINED WITH A REFRACTORY INORGANIC OXIDE IS ALSO DISCLOSED.

United States Patent O U.S. Cl. 252-442 4 Claims ABSTRACT OF THEDISCLOSURE Isomerizable hydrocarbons are isomerized using a catalytrccomposite comprising a combination of a platinum group component and atin component with a porous carrier material. A catalytic compositecomprising a platinum group metallic component, a tin component and aFriedel-Crafts metal halide component combined with a refractoryinorganic oxide is also disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of my copendmg application Ser. No. 807,910, filedMar. 14, 1969, the teachings of which are specifically incorporatedherein.

BACKGROUND OF THE INVENTION This invention relates to a process forisomerizing isomerizable hydrocarbons including isomerizable paraffins,cycloparafiins, olefins, and alkylaromatics. More particularly, thisinvention relates to a process for isomerizmg isomerizable hydrocarbonsWith a catalytic composite comprising a combination of platinum groupcomponent and a tin component with a porous carrier material. Moreprecisely, the present invention involves a dualfunction catalyticcomposite having both a hydrogenationdehydrogenation function and acracking function which enables substantial improvements in hydrocarbonisomerization processes that have traditionally used dual-functioncatalysts.

Isomerization processes for the isomerization of hydrocarbon haveacquired significant importance within in the petrochemical andpetroleum refining industry. The demand for the various xylene isomers,particularly para- Xylene, has resulted in a need for processes forisomerizing other xylene isomers and ethylbenzene to produce paraxylene.Also, the need for branched chain parafiins, such as isobutane orisopentane as intermediates for the production of high octane motor fuelalkylate can be met by isomerizing the corresponding normal paraflins.In addition, in motor fuel produced by parafiin-olefin alkylation, it isdesired that the final alkylate be highly branched to insure a highoctane rating. This can be accomplished by alkylating isobutane orisopentane with a C -C internal olefin which, in turn, can be producedby isomerization of the corresponding linear alpha-olefin and shiftingthe double 'bond to a more central position.

Catalytic composites exhibiting a dual hydrogenationdehydrogenationfunction and a cracking function are widely used in the petroleum andpetrochemical industry to isomerize isomerizable hydrocarbons. Thesecatalysts are generally characterized as having a heavy metal component,such as metals or metallic compounds of Group V through VIII of thePeriodic Table to impart a hydrogenation-dehydrogenation function whenassociated with an acid-acting, adsorptive, refractory inorganic oxidewhich imparts a cracking function. In these isomerization reactions, itis important that the catalytic composite not only catalyze the specificisomerization reaction involved by having its dualhydrogenation-dehydrogenation func- Patented Jan. 4, 1972 tion correctlybalanced against its cracking function, but further, that the catalystWill also be able to perform its desired functions equally well overprolonged periods of time.

The performance of a given catalyst in a hydrocarbon isomerizationprocess is typically measured by the activity, selectivity, andstability of the catalyst wherein activity refers to its ability toisomerize the hydrocarbon reactants into the corresponding isomers at aspecified set of reaction condition; selectivity refers to the percentreactants isomerized to form the desired isomerized product and/orproducts; and stability refers to the rate of change of the selectivityand activity of the catalyst.

The principal cause of instability (i.e. loss of selectivity andactivity in an original, selective, active catalyst) is the formation ofcoke on the catalytic surface of the catalyst during the course of thereaction; this coke being characterized as a high molecular weighthydrogen-deficient carbonaceous material, typically having an atomiccarbon to hydrogen ratio of about 1 or more. Accordingly, a majorproblem in the hydrocarbon isomerization art is the development of moreactive and selective composites that are not as sensitive to thepresence of the foregoing carbonaceous materials and/ or have theability to suppress the rate of the formation of these carbonaceousmaterials on the catalyst. A primary aim of the art is to develop ahydrocarbon isomerization process utilizing a dual-function catalysthaving superior activity, selectivity, and stability. In particular, itis desired to have a hydrocarbon isomerization process wherein theisomerizable hydrocarbons are isomerized without excessive cracking orother decomposition reactions occurring which lower the overall yield ofthe process and make it more difiicult to operate.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide a process for isomerizing isomerizable hydrocarbons. Morespecifically, it is an object of this invention to provide anisomerization process using a particular isomerization catalysteffective in isomerizing isomerizable hydrocarbons without introducingundesired decomposition and/ or cracking reactions. It is a furtherobject of this invention to provide a process for isomerizingisomerizable hydrocarbons utilizing a dual-function catalyst havingsuperior activity, selectivity and stability.

An isomerization process has now been developed utilizing adual-function catalyst which possesses improved activity, selectivity,and stability. Moreover, in the particular case of a C alkylaromaticisomerization process, this catalyst produces essentially equilibriumconversions of the C alkylaromatics with essentially stoichometricselectively without evidencing excessive production of hydrogenated orcracked products. Further, this activity and selectivity is readilymaintainable at its originally high levels, thus yielding a very stablecatalytic alkylaromatic isomerization process. This catalyst utilizes arelatively inexpensive component, tin, to promote a platinum metalcomponent when utilized with an acid-acting porous carrier material. I

In a broad embodiment, this invention relates to a process forisomerizing an isomerizable hydrocarbon which comprises contacting saidhydrocarbon at isomerization conditions with a catalytic compositecomprising a combination of a platinum group component and a tincomponent with a porous carrier material.

In a more limited embodiment, this invention relates to an isomerizationprocess utilizing a catalytic composite comprising a. combination of aplatinum component, a tin component, and a halogen component with analumina carrier material. These components are preferably present in thecomposite in amounts sufiicient to result in the final compositecontaining, on an elemental basis, about 0.1 to about 5.0 wt. percenthalogen, about 0.01 to about 1.0 wt. percent platinum, and about 0.01 toabout 5.0 wt. percent tin.

In a more specific embodiment, this invention relates to theisomerization of either saturated or olefinic isomerizable hydrocarbonsby contacting either hydrocarbon with the aforementioned catalyticcomposites at isomerization conditions which include a temperature ofabout C. to about 425 C., a pressure of about atmospheric to about 100atmospheres and a liquid hourly space velocity of about 0.1 to about 10.In another limited embodiment this process relates to the isomerizationof an isomerizable alkylaromatic hydrocarbon by contacting thealkylaromatic with the aforementioned catalytic composites atisomerization conditions which include a temperature of about 0 C. toabout 600 C., a pressure of about atmospheric to about 100 atmospheres,a liquid hourly space velocity of about 0.1 to about 20.0 hr.- and ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1.

In another embodiment, this invention relates to a catalytic compositewhich comprises a refractory inorganic oxide having combined therewith aplatinum group metallic component, a tin component, and a Friedel-Crafts metal halide component.

Other objects and embodiments referring to alternative isomerizablehydrocarbons and to alternative catalytic compositions will be found inthe following further detailed description of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of this inventionis applicable to the isomerization of isomerizable saturatedhydrocarbons including acylic parafiins and cyclic naphthenes and isparticularly suitable for the isomerization of straight chain or mildlybranched chain paraffins containing 4 or more carbon atoms per moleculesuch as normal butane, normal pentane, normal hexane, normal heptane,normal octane, etc. and mixtures thereof. Cycloparalfins applicable arethose ordinarily containing at least 5 carbon atoms in the ring such asalkylcyclopentanes and cyclohexanes, including methylcyclopentane,dimethylcyclopentane, cyclohexane, methylcyclohex-ane,dimethylcyclohexane, etc. This process also applies to the conversion ofmixtures of parafiins and/or naphthenes such as those derived byselective fractionation and distillation of straight-run naturalgasolines and naphthas. Such mixtures of parafiins and/or naphthenesinclude the so-called pentane fractions, hexane fractions, and mixturesthereof. It is not intended, however, to limit this invention to theseenumerated saturated hydrocarbons and it is contemplated that straightor branched chain saturated hydrocarbons containing up to about 20carbon atoms per molecule may be isomerize'd according to the process ofthe present invention with C C hydrocarbons being particularlypreferred.

The olefins applicable within this isomerization process are generally amixture of olefinic hydrocanbons of approximately the same molecularweight, including the l-isomer, 2-isomer, and other position isomers,capable of undergoing isomerization to an olefin in which the doublebond occupies a more centrally located position in the hydrocarbonchain. The process of this invention can be used to provide an olefinicfeedstock for motor fuel alkylation purposes containing an optimumamount of the more centrally located double bond isomers, by convertingthe l-isomer, or other near terminal position isomer into olefinswherein the double bond is more centrally located in the carbon atomschain. The process of this invention is also applicable to theisomerization of such isomerizable olefinic hydrocarbons such as theisomerization of l-butene to 2-butene or the isomerization of the3-methyl-1- butene to 2-methyl-2-butene. Also, the process of thisinvention can be utilized to shift the double bond of an olefinichydrocarbon such as l-pentene, l-hexene, Z-hexene,

and 4-methyl-1-pentene to a more centrally located position so thatZ-pentene, 2-hexene, 3-hexene and 4-methyl- 2-pentene, respectively, canbe obtained. It is not intended to limit this invention to theseenumerated olefinic hydrocarbons as it is contemplated that shifting ofthe double bond to a more centrally located position may be effective instraight or branched chain olefinic hydrocarbons containing up to about20 carbon atoms per molecule. The process of this invention also appliesto the hydroisomerization of olefins wherein olefins are converted tobranchedchain paraffins and/or branched olefins.

Further, the process of this invention is also applicable to theisomerization of isomerizable alkylaromatic hydrocarbons includingorthoxylene, metaxylene, paraxylene, ethylbenzene, the ethyltoluenes,the trimethylbenzenes, the diethylbenzenes, the triethylbenzenes, normalpropyl benzene, isopropylbenzene, etc., and mixtures thereof. Preferredisomerizable alkylaromatic hydrocarbons are the monocyclic alkylaromatichydrocarbons, that is, the alkyl benzene hydrocarbons, particularly theC alkylbenzenes, and non-equilibrium mixtures of the various C aromaticisomers. Higher molecular weight alkylaromatic hydrocarbons such as thealkylnaphthalenes, the alkylanthracenes, the alkylphenanthrenes, etc.,are also suitable.

These foregoing isomerizable hydrocarbons may be derived as selectivefractions from various naturallyoccuring petroleum streams either asindividual components or as certain boiling range fractions obtained bythe selective fractionation and distillation of catalytically crackedgas oil. Thus, the process of this invention may be successfully appliedto and utilized for complete conversion of isomerizable hydrocarbonswhen these isomerizable hydrocarbons are present in minor quantities invarious fluid or gaseous streams. Thus, the isomerizable hydrocarbonsfor use in the process of this invention need not be concentrated. Forexample, isomerizable hydrocarbons appear in minor quantities in variousrefinery streams, usually diluted with gases such as hydrogen, nitrogen,methane, ethane, propane, etc. These refinery streams containing minorquantities of isomerizable hydrocarbons are obtained in petroleumrefineries and various refinery installations including thermal crackingunits, catalytic cracking units, thermal reforming units, coking units,polymerization units, dehydrogenation units, etc. Such refineryotfstreams have in the past been burned for fuel value, since aneconomical process for the utilization of the hydrocarbon content hasnot been available. This is particularly true for refinery fluid streamsknown as off gas streams containing minor quantities of isomerizablehydrocarbons. In addition, this process is capable of isomerizingaromatic streams, such as reformate, to produce xylenes, particularlypara-xylene, thus upgrading the reformate from its gasoline value to ahigh petrochemical value.

As hereinnbefore indicated, the catalyst utilized in the process of thepresent invention comprises a porous carrier material or support havingcombined therewith a platinum group component, a tin component, and inthe preferred case, a halogen component. Considering first the porouscarrier material utilized in this catalyst, it is preferred that thematerial be a porous, adsorptive, highsurface area support having asurface area of about 25 to about 500 m. gm. The porous carrier materialshould be relatively refractory to the conditions utilized in thehydrocarbon conversion process, and it is intended to include within thescope of the process of the present invention, carrier materials whichhave traditionally been utilized in dual-function hydrocarbon conversioncatalysts such as: (1) activated carbon, coke, or charcoal; (2) silicaor silica gel, clays and silicates including those syntheticallyprepared and naturally-occurring, which may or may not be acid treated,such as for example, Attapul us clay, china, clay, diatomaceous earth,fullers earth, kaolin, kieselguhr, etc.; (3) ceramics, porcelain,crushed firebrick,

and bauxite; (4) refractory inorganic oxides such as alumina, titaniumdioxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia,thoria, boria, silica-alumina, silica-magnesia, chromia-alumina,alumina-boria, silicazirconia, etc.; (5) crystalline aluminosilicates(also a refractory inorganic oxide) such as naturally-occurring orsynthetically-prepared mordenite and/or faujasite, either in thehydrogen form or in a form which has been treated with multi-valentcations; and, (6) combinations of these foregoing carrier materials. Thepreferred porous carrier materials for use in the present invention arerefractory inorganic oxides with best results obtained with an aluminacarrier material. Suitable alumina materials are the crystallinealuminas known as the gamma-, eta-, and theta-alumina with gammaoreta-alumina giving best results. In addition, in some embodiments thealumina carrier material may contain minor proportions of other wellknown refractory inorganic oxides such as silica, zirconia, magnesia,etc.; however, the preferred support is substantially pure gammaoreta-alumina. The preferred carrier materials have an apparent bulkdensity of about 0.30 to about 0.70 gm./ cc. and surface areacharacteristics such that the average pore diameter is about 20 to 300angstroms, the pore volume is about 0.10 to about 1.0 ml./ gm. and thesurface area is about 100 to about 500 mF/gm. In general, best resultsare typically obtained with a gamma-alumina carrier material which isused in the form of spherical particles having a relatively smalldiameter (i.e. typically about inch), an apparent bulk density of about0.5 gm./cc., a pore volume of about 0.4 ml./ gm. and a surface area ofabout 175 m. gm.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminasupport may be prepared by adding a suitable alkaline reagent, such aammonium hydroxide to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The alumina maybe formed in any desired shape such as spheres, pills, cakes,extrudates, powders, granules, etc., and utilized in any desired size.For the purpose of the present invention a particularly preferred formof alumina is he sphere. Alumina spheres may be continuouslymanufactured by the well known oil drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe hydrosol with a suitable gelling agent and dropping the resultantmixture into an oil bath maintained at elevated temperatures. Thedroplets of the mixture remain in the oil bath until they set and formhydrogel spheres. The spheres are then continuously withdrawn from theoil bath and typically subjected to specific aging treatments in oil andan ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300 F. to about 400F. and then subjected to a calcination procedure at a temperature ofabout 850 F. to about 1300 F. for a period of about 1 to about 20 hours.This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See US. Pat. No. 2,620,314 foradditional details.

An essential constituent of the catalyst of the present invention is atin component. This component may be present as an elemental metal or asa chemical cornpound such as the oxide, sulfide, halide, etc. Thiscomponent may be incorporated in the catalytic composite in any suitablemanner such as by coprecipitation or cogellation with the porous carriermaterial, ion exchange with the carrier material or impregnation of thecarrier material at any stage in the preparation. It is to be noted thatit is intended to include Within the scope of the process of the presentinvention all conventional methods for incorporating a metalliccomponent in a catalytic composite, and the particular method ofincorporation used is not determined to be an essential feature of thepresent invention. One preferred method of incorporating the tincomponent into the catalytic composite involves coprecipitating the tincomponent during the preparation of the preferred refractory oxidecarrier material. In the preferred case, this involves the addition ofsuitable soluble tin compounds such as stannous or stannic halide to thealumina hydrosol, and then combining the hydrosol with a suitablegelling agent, and dropping the resulting mixture into an oil bath,etc., as hereinbefore explained in detail. Following the calcinationstep, there is obtained a carrier material comprising an intimatecombination of alumina and stannic oxide. Another pre ferred method ofincorporating the tin component into the catalyst composite involves theutilization of a watersoluble compound of tin to impregnate the porouscarrier material. Thus, the tin component may be added to the carriermaterial by commingling the latter with an aqueous solution of asuitable tin salt or water-soluble compound of tin such as stannousbromide, stannous chloride, stannic chloride, stannic chloridepentahydrate, stannic chloride tetrahydrate, stannic chloridetrihydrate, stannic chloride diamine, stannic trichloride bromide,stannic chromate, stannous fluoride, stannic fluoride, stannic iodide,stannic sulfate, stannic tartrate, and the like compounds. Theutilization of a tin chloride com pound, such as stannous or stannicchloride, is particularly preferred since it facilitates theincorporation of both the tin component and at least a minor amount ofthe preferred halogen component in a single step. In general, the tincomponent can be impregnated either prior to, simultaneously .with, orafter the platinum group metallic component is added to the carriermaterial. However, I have found that excellent results are obtained whenthe tin component is impregnated simultaneously with the platinum groupmetallic component. In fact, I have determined that a preferredimpregnation solution contains chloroplatinic acid, hydrogen chloride,and stannous or stannic chloride. Following the impregnation step, theresulting composite is typically dried and calcined as explainedhereinafter.

As indicated above, the catalyst utilized in the proc ess of the presentinvention also contains a platinum group component. Although the processof the present invention is specifically directed to the use of acatalytic composite containing platinum, it is intended to include otherplatinum group metals such as palladium, rhodium, ruthenium, osmium, andiridium, particularly palladium. The platinum group component, such asplatinum, may exist within the final catalytic composite as a compoundsuch as an oxide, sulfide, halide, etc., or as an elemental state.Generally, the amount of the platinum group component present in thefinal catalyst composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally comprises about 0.05 to about 1.0 wt. percent of thefinal catalytic composite, calculated m an elemental basis. Excellentresults are obtained when the catalyst contains about 0.3 to about 0.9wt. percent of the platinum group metal. The preferred platinum groupcomponent is platinum or a compound of platinum.

The platinum group component may be incorporated in the catalyticcomposite in any suitable manner such as coprecipitation or cogellationwith the preferred carrier material, ion-exchange, or impregantion. Thepreferred method of preparing the catalyst involves the utilization of awater-soluble compound of a platinum group metal to impregnate thecarrier material. Thus, the platinum group component may be added to thesupport by commingling the latter with an aqueous solution ofchloroplatinic acid. Other water-soluble compounds of platinum may beemployed in impregnation solutions and include ammonium chloroplatinate,platinum chloride, dinitro diamino platinum, etc. The utilization of aplatinum chlo ride compound, such as chloroplatinic acid, is preferredsince it facilitates the incorporation of both the platinum componentand at least a minor quantity of the preferred halogen component in asingle step. Hydrogen chloride is also generally added to theimpregnation solution in order to further facilitate the incorporationof the halogen component. In addition, it is generally preferred toimpregnate the carrier material after it has been calcined in order tominimize the risk of washing away the valuable platinum metal compounds;however, in some cases it may be advantagous to impregnate the carriermaterial when it is in a gelled state. Following the impregnation, theresulting impregnated support is dried and subjected to a hightemperature calcination or oxidation technique which is explainedhereinafter.

Although it is not essential, it is generally preferred to incorporate ahalogen component into the catalytic composite utilized in the processof the present invention to impart additional acidity and activity tothe catalyst. Accordingly, a preferred embodiment of the presentinvention involves a catalytic composite comprising a combination of aplatinum group metallic component, a tin component, and a halogencomponent with an alumina carrier material. Although the precise form ofthe chemistry of the association of the halogen component with thecarrier material is not entirely known, it is customary in the art torefer to the halogen component as being combined with the carriermaterial, or with the other ingredients of the catalyst. This combinedhalogen may be either flu orine, chlorine, iodine, bromine, or mixturesthereof. Of these, fluorine and, particularly, chlorine are preferredfor the purposes of the present invention either singly or incombination with each other. The halogen may be added to the carriermaterial in any suitable manner, either during preparation of thesupport or before, during or after the addition of the other components.For example, the halogen may be added, at any stage of the preparationof the carrier material or to the calcined carrier material, as anaqueous solution of an acid such as hydrogen fluoride, hydrogenchloride, hydrogen bromide, etc. The halogen component or a portionthereof, may be composited with the carrier material during theimpregnation of the latter with the platinum group component; for example, through the utilization of a mixture of chloroplatinic acid andhydrogen chloride. In another situation, the alumina hydrosol which istypically utilized to form the preferred alumina carrier material maycontain halogen and thus contribute at least a portion of the halogencomponent to the final composite. For use in an isomerization process,the halogen will be typically combined with the carrier material in anamount suflicient to result in a final composite that contains about0.1% to about 10.0 wt. percent and preferably about 0.1 to about 5.0total weight percent halogen, calculated on an elemental basis. Inparticular, about 0.2 to about 1.5 percent by weight chlorine and/orabout 0.5 to about 3.5 percent by weight fluorine yield a veryeffective, stable isomerization catalyst. In addition, small amounts ofchloride or fluoride may be continuously added to the catalyst to offsetany halogen loss by commingling a halogen containing compoundi.e. CCL;with the hydrocarbon feed.

Regarding the amount of the tin component contained in the catalystutilized in the process of this invention, it is preferably about 0.01to about 5.0 Wt. percent tin, calculated on an elemental basis, althoughsubstantially higher amounts of tin may be utilized in some cases. Inthe case where the tin component is incorporated in the catalyst bycoprecipitating it with the preferred alumina carrier material, it iswithin the scope of the present invention to prepare catalystscontaining up to 30 wt. percent tin calculated on an elemental basis.Regardless of the absolute amounts of the tin component and the platinumgroup component utilized, the atomic ratio of the platinum group metalto the tin metal contained in the catalyst is preferably selected fromthe range of about .121 to about 3:1 with best results achieved at anatomic ratio of about 0.5 :1 to 1.5 :1. This is particularly true whenthe total content of the tin component plus the platinum group metalliccomponent in the catalytic composite is fixed in the range of about .15to about 2.0 wt. percent thereof, calculated on an elemental tin andplatinum group metal basis. Accordingly, examples of especiallypreferred catalytic composites are as follows: (1) a catalytic compositecomprising 0.5 wt. percent tin and 0.75 wt. percent platinum combinedwith an alumina carrier material, (2) a catalytic composite comprising.1 wt. percent tin and .65 wt. percent platinum combined with an aluminacarrier material, (3) a catalytic composite comprising .375 wt. percenttin and .375 wt. percent platinum combined with an alumina carriermaterial, (4) a catalytic composite comprising 1.0 wt. percent tin plus0.5 wt. percent platinum combined with an alumina carrier material, and,(5) a catalytic composite com prising 0.25 wt. percent tin and 0.5 Wt.percent platinum combined with an alumina carrier material. In anisomerization process, it is generally preferred to also include in thecatalytic composite a halogen component in an amount of 0.1 to about10.0 wt. percent as explained hereinbefore. Accordingly, an especiallypreferred catalytic composite for use in the isomerization process ofthis invention comprises a combination of a platinum component, a tincomponent, and a halogen component with an alumina carrier material inamounts sufficient to result in the catalyst containing, on an elementalbasis, about 0.1 to about 10.0 wt. percent halogen, about 0.01 to about1.0 wt. percent platinum, and about 0.01 to about 5.0 wt. percent tin.In this isomerization process best results are obtained when the halogencomponent is chlorine, fluorine or a compound of chlorine or fluorine,and the catalyst contains about 0.1 to about 1.0 wt. percent tin,calculated on an elemental basis.

Regardless of the details of how the components of the catalyst utilizedin the process of this invention are combined with the porous carriermaterial, the final catalyst generally will be dried at a temperature ofabout 200 to about 600 F. for a period of from about 2 to about 24 hoursor more, and finally calcined at a temperature of about 700 F. to about1100 F. in an air atmosphere for a period of about 0.5 to about 10 hoursin order to convert the metallic components substantially to the oxideform. In the case where a halogen component is utilized in the catalyst,best results are generally obtained when the halo gen content of thecatalyst is adjusted during the calcination step by including a halogenor a halogen-containing compound in the air atmosphere utilized. Inparticular, when the halogen component of the catalyst is chlorine, itis preferred to use a mole ratio of H 0 to HCl of about 20:1 to about :1during at least a portion of the calcination step in order to adjust thefinal chlorine content of the catalyst to a range of about 0.2 to about1.5 wt. percent.

Although not essential, the resulting calcined catalytic composite canbe impregnated with an anhydrous Friedel- Crafts type metal halide,particularly aluminum chloride. Other suitable metal halides includealuminum bromide, ferric chloride, ferric bromide, zinc chloride,beryllium chloride, etc. It is preferred that the porous carriermaterial contain chemically combined hydroxyl groups such as thosecontained in silica and any of the other aforementioned refractoryinorganic oxides including the various crystalline aluminosilicates andclays. Particularly preferred is alumina.

The presence of chemically combined hydroxyl groups in the porouscarrier material allows a reaction to occur between the Friedel-Craftsmetal halide and the hydroxyl groups of the carrier. For example,aluminum chloride reacts with the hydroxyl groups of alumina to yieldactive centers which enhance the catalytic behavior of the originalplatinum-tin-alumina composite, particularly for isomerizing Cparaffins.

The Friedel-Crafts metal halide can be impregnated onto a calcinedcatalytic composite containing combined hydroxyl groups by thesublimation of the halide onto the tin-platinum composite underconditions such that the sublimed metal halide is combined with thehydroxyl groups of the composite. This reaction is accompanied by theelimination of from about 0.5 to about 2.0 moles of hydrogen chlorideper mole of Friedel-Crafts metal halide reacted. For example, in thecase of sublirning aluminum chloride which sublimes at about 184 0.,suitable impregnation temperatures range from about 190 C. to about 7000., preferably from about 200 C. to about 600 C. The sublimation can beconducted at atmospheric pressure or under increased pressures and inthe presence of diluents such an inert gases, hydrogen and/ or lightparafi'inic hydrocarbons. The impregnation may be conducted batchwisebut a preferred method is to pass sublimed AlCl vapors in admixtureswith an inert gas such as hydrogen through a calcined catalyst bed. Thismethod both continuously deposits the AlCl and removes the evolved HCl.

The amount of metal halide combined with a tin-plati num composite mayrange from about 1% to about 100% of the original metal halide-freecomposite. The final composite has unreacted metal halide removed bytreating the composite at a temperature above the sublimationtemperature of the halide for a time sutficient to remove therefrom anyunreacted metal halide. For AlCl temperatures of about 400 C. to about600 C. and times of from about 1 to about 48 hours are satisfactory.

Although it is not essential, it is preferred that the calcinedcatalytic composite be subjected to a substantially water-free reductionstep prior to its use in the isomerization of hydrocarbons. This step isdesigned to insure a uniform and finely divided dispersion of themetallic component throughout the carrier material. Preferably,substantially pure and dry hydrogen (i.e., less than 20 vol. p.p.m. H O)is used as the reducing agent in this step. The reducing agent iscontacted with the calcined catalyst at a temperature of about 800 F. toabout 1200 F. and for a period of time of about 0.5 to hours or moreeffective to substantially reduce both meallic components to theirelemental state. This reduction treatment may be performed in situ aspart of a start-up sequence if precautions are taken to predry the plantto a substantially water-free state and if substantially water-freehydrogen is used.

The resulting reduced catalytic composite may, in some cases, bebeneficially subjected to a presulfiding operation designed toincorporate in the catalytic composite from about 0.05 to about 0.50 wt.percent sulfur calculated on an elemental basis. Preferably, thispresulfiding treatment takes place in the presence of hydrogen and asuitable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the reduced catalyst with a sulfiding gassuch as a hydrogen-hydrogen sulfide mixture having about 10 moles ofhydrogen present per mole of hydrogen sulfide at conditions sufficientto effeet the desired incorporation of sulfur, generally including atemperature ranging from about 50 F. up to about 1100 F. or more. It isgenerally a good practice to perform this presulfiding step undersubstantially water-free conditions.

According to the process of the present invention, a

hydrocarbon charge stock, preferably in admixture with hydrogen arecontacted with a catalyst of the type hereinbefore described in ahydrocarbon isomerization zone. This contacting may be accomplished byusing the catalyst in a fixed bed system, a moving bed system, afluidized bed system, or in a batch type operation; however, in view ofthe danger of attrition losses of the valuable catalyst and of wellknown operational advantages, it is preferred to use a fixed bed system.In this system, a hydrogen-rich gas and the charge stock are preheatedby any suitable heating means to the desired reaction temperature andthen are passed into an isomerization zone containing a fixed bed of thecatalyst type previously characterized. It is, of course, understoodthat the conversion zone may be one or more separate reactors withsuitable means therebetween to insure that the desired isomerizationtemperature is maintained at the entrance to each reactor. It is also tobe noted that the reactants may be contacted with the catalyst bed ineither upward, downward, or radial flow fashion. In addition, it is tobe noted that the reactants may be in the liquid phase, a mixedliquid-vapor phase, or a vapor phase when contacted with the catalystwith best results obtained in a vapor phase.

The process of this invention, utilizing the catalyst hereinbefore setforth, for isomerizing isomerizable olefinic or saturated hydrocarbonsis preferably effected in a continuous down-flow fixed bed system. Oneparticular method is continuously passing the hydrocarbon preferablycommingled with about 0.1 to about 10 moles or more of hydrogen per moleof hydrocarbon to an isomerization reaction zone containing the catalystand maintaining the zone at proper isomerization conditions such as atemperature in the range of about 0 to about 425 C. or more and apressure of about atmospheric to about atmospheres or more. Thehydrocarbon is passed over the catalyst at a liquid hourly spacevelocity (defined as volume of liquid hydrocarbon passed per hour pervolume of catalyst) of from about 0.1 to about 10 hr." or more. Inaddition, diluents such as argon, nitrogen, etc. may be present. Theisomerized product is continuously withdrawn, separated from the reactoreffiuent, and recovered by conventional means, preferably fractionaldistillation, while the unreacted starting material may be recycled toform a portion of the feed stock.

Likewise, the process of this invention for isomerizing an isomerizablealkylaromatic hydrocarbon is preferably effected by contacting thearomatic, in a reaction zone containing the hereinbefore describedcatalyst, with a fixed catalyst bed by passing the hydrocarbon in adown-flow fashion through the bed while maintaining the zone at properalkylaromatic isomerization conditions such as a temperature in therange from about 0 C. to about 600 C. or more, and a pressure ofatmospheric to about 100 atmospheres or more. The hydrocarbon is passed,preferably in admixture with hydrogen at a hydrogen to hydrocarbon moleratio of about 1:1 to about 25:1 or more, at a liquid hourly hydrocarbonspace velocity of about 0.1 to about 20 hr.- or more. Other inertdiluents such as nitrogen, argon, etc., may be present. The isomerizedproduct is continuously withdrawn, separated from the reactor efiluentby conventional means including fractional distillation orcrystallization and recovered.

EXAMPLES The following examples are given to illustrate the preparationof the catalytic composite to be utilized in the process of thisinvention and its use in the isomerization of isomerizable hydrocarbons.However, those examples are not presented for purposes of limiting thescope of the invention but in order to further illustrate theembodiments of the present process.

1 1 EXAMPLE I This example demonstrates a method of preparing thepreferred catalytic composite to be utilized in the process of thepresent invention.

An alumina carrier material comprising spheres was prepared by: formingan alumina hydroxyl chloride sol by dissolving substantially purealuminum pellets in a hydrochloric acid solution, addinghexamethylenetetramine to the resulting sol, gelling the resultingsolution by dropping it into an oil bath to form spherical particles ofan aluminum hydrogel, aging, and washing the resulting particles, andfinally drying and calcining the aged and washed particles to formspherical particles of gamma-alumina containing about 0.3 wt. percentcombined chloride. Additional details as to this method of preparing thepreferred carrier material are given in the teachings of U.S. Pat. No.2,620,314.

The resulting gamma-alumina particles were then contacted with animpregnation solution containing chloroplatinic acid, hydrogen chlorideand stannic chloride in amounts sufficient to yield a final compositecontaining 0.75 wt. percent platinum and 0.5 wt. percent tin, calculatedon an elemental basis. The impregnated spheres were then dried at atemperature of about 300 F. for about an hour and thereafter calcined inan air atmosphere at a temperature of about 925 F. for about 1 hour. Theresulting calcined spheres were then contacted with an air streamcontaining H and HCl in a mole ratio of about 40:1 for about 4 hours at975 F.

The resulting catalyst particles were analyzed and found to contain, onan elemental basis, about 0.75 wt. percent platinum, about 0.5 wt.percent tin, and about 0.85 wt. percent chloride. The resulting catalystis designated catalyst A.

EXAMPLE II This example illustrates an alternative method for preparingthe preferred catalytic composite of the present invention.

An alumina hydroxyl chloride sol was prepared by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution.Thereafter, an amount of stannic chloride calculated to provide a finalcatalyst containing 0.5 wt. percent tin was dissolved in this sol.Hexamethylenetetramine was then added to the resulting mixture to form adropping solution which was subsequently gelled by dropping it into anoil bath in a manner selected to form spherical particles of an aluminumhydrogel having an average diameter of about The resulting sphericalhydrogel particles were then aged and washed in an ammoniacal solution,and thereafter dried and calcined to form gamma-alumina particlescontaining 0.3 wt. percent combined chloride and approximately 0.5 wt.percent tin. Additional details as to the mechanics associated with thismethod of carrier material preparation are given in the teachings ofU.S. Pat. No. 2,620,314.

The resulting particles comprised an intimate combination of tin oxidewith alumina. They were then impregnated with an aqueous solutioncontaining chloroplatinic acid and hydrogen chloride in amountssufficient to yield a final composite containing about 0.75 wt. percentplatinum. The impregnated spheres were then dried at a temperature ofabout 300 F. for about 1 hour and calcined in an air atmosphere at atemperature of about 975 C. for about 1 hour. Thereafter, the resultingcalcined spheres were subjected to contact with an air stream containingH 0 and HCl in a mole ratio of about 40:1 for about 4 hours at about 975F.

Thereafter, the spheres were subjected to a dry prereduction treatmentby contacting them with a substantially pure hydrogen stream containingsubstantially less than 20 vol. p.p.m. H O at a temperature of about1025 F a pressure slightly above atmospheric, and a flow rate of thehydrogen stream through the catalyst particles corresponding to a gashourly space velocity of about 720 hr." for a period of about 1 hour.The resulting prereduced catalyst was then contacted with asubstantially water-free gaseous mixture of H and H 8 of about 10:1 H toH 8 mole ratio at conditions substantially identical to those usedduring the pre-reduction step.

The resulting catalyst was analyzed and found to contain, on anelemental basis, 0.75 wt. percent platinum, about 0.5 wt. percent tin,about 0.85 wt. percent chloride, and about 0.1 wt. percent sulfur. It ishereinafter designated catalyst B. The principal distinctions betweencatalyst B and catalyst A relate to their method of preparation (the tincomponent was incorporated in catalyst A by simultaneous impregnationand in catalyst B by coprecipitation with the carrier material) and tothe pretreatment performed thereon (i.e. catalyst A was not pre-reducedand sulfided and is used in the oxidized form with subsequent reductionin situ during start-up, whereas catalyst B was pre-reduced andsulfided).

EXAMPLE III A portion of the catalyst prepared in Example I anddesignated as catalyst A is placed, as a catalytic composite, in acontinuous flow fixed bed isomerization plant of conventional design.The charge stock, containing on a wt. percent basis, 20.0% ethylbenzene,10.0% paraxylene, 50.0% meta-xylene, and 20.0% ortho-xylene iscommingled with about 8 moles of hydrogen per mole of hydrocarbon,heated to 400 C., and continuously charged at 4.0 hr.- liquid hourlyspace velocity (LHSV) to the reactor which is maintained at a pressureof about 400 p.s.i.g. and 400 C. The resulting product evidencesessentially equilibrium conversion to para-xylene with onlyinsignificant amounts of cracked products thus indicating an efiicientalkylaromatic isomerization catalyst.

EXAMPLE IV A portion of the catalyst prepared in Example II anddesignated as catalyst B is also placed in a continuousflow fixed-bedisomerization plant of conventional design. The same charge stockutilized in Example III is charged, at the same conditions employed inExample III, to the reactor. The resulting product evidences essentiallyequilibrium conversion to para-xylene and only insignificant amounts ofcracked products with essentially the same yields as obtained in ExampleIII thus indicating that catalyst A and catalyst B, diifering only intheir method of preparation, are essentially equivalent isomerizationcatalysts.

EXAMPLE V A portion of the catalyst produced by the method of Example I(catalyst A) is placed in a continuous flow, fixed bed isomerizationplant of conventional design as utilized in Examples III and IV.Substantially pure meta xylene is used as a charge stock. The chargestock is commingled with about 8 moles of hydrogen per mole of chargedto the reactor which is maintained at a pressure hydrocarbon, heated toabout 390 C., and continuously of about 300 p.s.i.g. Substantialconversion of meta-xylene to para-xylene is obtained i.e. greater thanof equilibrium.

EXAMPLE VI A catalyst identical to that produced in Example I butcontaining only 0.40 wt. percent combined chloride is used to isomerizel-butene in an appropriate isomeriza tion reactor, at a reactor pressureof about 500 p.s.i.g. and a reactor temperature of about C. Substantialconversion to Z-butene is observed.

EXAMPLE VII The same catalyst as utilized in Example VI is charged to anappropriate, continuous isomerization reactor of conventional designmaintained at a reactor pressure of about 1000 p.s.i.g. and a reactortemperature of about 13 180 C. 3-methyl-1-butene is continuously passedto this reactor with substantial conversion to 2-methyl-2- butene beingobserved.

EXAMPLE VIII A catalyst, identical to that catalyst produced in ExampleI except that the gamma-alumina particles are contacted with hydrogenfluoride to provide a 2.9 wt. percent combined fluoride content in thecatalyst, is placed in an appropriate continuous isomerization reactorof conventional design maintained at a reactor pressure of about 300p.s.i.g. and a reactor temperature of about 200 C. Normal hexane iscontinuously charged to the reactor and an analysis of the productstream shows substantial conversion to2,2-dimethylbutame-2,3-dimethylbutane-2-methylpentane, and3-methylpentane.

EXAMPLE IX 200 grams of the reduced platinum-tin-aluminum composite ofExample I are placed in a glass-lined rotating autoclave along with 150grams of anhydrous aluminum chloride. The autoclave is sealed, pressuredwith 25 p.s.i.g. of hydrogen and heated and rotated for 2 hours at 300C. The autoclave is then allowed to cool, depressured through a causticscrubber, opened and the final composite removed therefrom. An analysisof this composite indicates a wt. percent gain based on the originalcomposite, equivalent to the aluminum chloride sublimed and reactedthereon. The caustic scrubber is found to have absorbed hydrogenchloride equivalent to about 5.0 wt. percent of the original compositecorresponding to about 0.8 moles of HCl evolved per mole of aluminumchloride adsorbed.

EXAMPLE X A portion of the catalyst prepared in Example IX is placed inan appropriate continuous isomerization apparatus and used to isomerizenormal butane at a reactor pressure of 300 p.s.i.g., a 0.5 hydrogen tohydrocarbon mole ratio, a 1.0 liquid hourly space velocity, and areactor temperature of 230 C. Substantial conversion of normal butane toisobutane is observed i.e. approximately a conversion of normal butaneto isobutane of about 45 wt. percent of the original butane charged.

1 4 EXAMPLE XI A portion of the catalyst as prepared in Example I isplaced in an appropriate continuous isomerization reactor maintained ata reactor temperature of about 210 C. and a reactor pressure of about250 p.s.i.g. Methylcyclopentane is continuously passed to this reactorwith a substantial conversion to cyclohexane being observed.

I claim as my invention:

1. A catalytic composite which comprises a refractory inorganic oxidehaving combined therewith a platinum group component, tin, and aFriedel-Crafts metal halide component, said composite containing, on aFriedel- Crafts metal halide-free basis, about 0.01 to about 1.0 Wt.percent platinum group metal and about 0.01 to about 5 .0 Wt. percenttin,

substantially all of said tin being present as the elemental metal, andabout 1.0 to about wt. percent Friedel-Crafts metal halide in which themetal is selected from the group consisting of aluminum, iron, zinc andberyllium.

2. The composite of claim 1 further characterized in that said platinumgroup metal is platinum, palladium or a compound of platinum orpalladium.

3. The composite of claim 2 further characterized in that said metalhalide is anhydrous aluminum chloride.

4. The composite of claim 1 wherein a sulfur component is combinedtherewith in an amount based on elemental sulfur of about 0.05 to about0.5 wt. percent of the metal halide-free composite.

References Cited UNITED STATES PATENTS 3,165,479 1/1965 Burk et al252-466 3,231,517 1/1966 Bloch et a1. 252-442 CURTIS R. DAVIS, PrimaryExaminer U.S. Cl. X.R.

